Presently, an importance in relation to the environment has become a predominant issue, and according to the global trends, regulations on exhaust gas of a construction machine have become stricter. For example, as standards regarding a discharge of exhaust gas of the construction machine such as a wheel loader, Stage IIIb, Stage IV, and the like that are emission standards of the European Union (EU), and Tier 4 standard and the like that are emission environmental standards of North America are adopted at present or will be adopted.
Meanwhile, unlike the existing regulations on exhaust gas that restricts only the exhaust gas in a steady state, the regulations on exhaust gas, which will be enforced later, also restricts the exhaust gas in a transient state.
For example, because there are no regulations on exhaust gas in the transition state (for example, acceleration state) under the existing regulations, an arbitrary amount of fuel could be injected without limitation with respect to an injection amount of fuel during an acceleration. That is, acceleration performance of the construction machine may be efficiently raised by raising the injection amount of fuel during the acceleration of the construction machine.
However, according to the regulations that will be enforced later, the above method may not be used any longer. For example, the existing method in which the acceleration performance is freely raised by increasing the injection amount of fuel may not be used any longer, and therefore, in order to improve the acceleration performance, a method is considered which reduces a load of a working system or the like except for a load of a traveling system among loads applied to the engine. The reason why the load of the traveling system is excluded is that as a result of reducing the load of the traveling system, the acceleration performance is reduced.
For example, the torque of the engine may be classified into torque of a traveling system, torque of a working system (or torque for front work), torque of a fan, torque of an accessory, and the like, and therefore, it is necessary to reduce the other torque except for the torque of the traveling system among the above torque.
For example, the method of the related art, which reduces the torque of the working system, may be a power shift control that is used in the construction machine such as the existing excavator. FIGS. 1 and 2 are flow charts exemplarily illustrating a method of controlling a power shift in the related art, respectively.
The method of controlling the power shift in the related art as illustrated in FIG. 1 is characterized in that first, the number of revolutions of the engine is detected in real time (S10), it is determined whether a variation amount of the number of revolutions of the engine exceeds a specific value (for example, a) (S12), and then when the variation amount thereof exceeds the specific value (YES), the flow rate of the pump of the working system is controlled (reduced) (S14), and when the variation amount thereof does not exceed the specific value (NO), the flow rate of the pump of the working system is controlled so as to be the maximum flow rate (S16). Here, the operation of controlling the pump flow rate so as to be the maximum flow rate means an operation of controlling the pump of the working system so that all working oil may be discharged at a flow rate that is required for the pump of the working system under control by an operator or equipment.
That is, the method is a method of, when the number of revolutions of the engine is reduced due to external force, adjusting the torque of the working machine by, for example, adjusting an angle of a swash plate of the pump of the working system in accordance with the variation amount of the number of revolutions. The method is a method capable of efficiently controlling the pump of the working system against the torque generated due to external force, but is not appropriate as a method of adjusting torque when the construction machine such as the wheel loader accelerates. For example, the reason is that because the variation amount of the number of revolutions of the engine is not reduced when the wheel loader accelerates, excessive torque under the acceleration condition may not be efficiently detected.
Further, the method of controlling the power shift in the related art as illustrated in FIG. 2 is characterized in that first, the number of revolutions of the engine is detected in real time (S20), it is determined whether the number of revolutions of the engine is below a specific value (for example, b) (S22), and then when the number of revolutions thereof is below the specific value (YES), a flow rate of a fan pump is controlled (reduced) (S24), and when the number of revolutions thereof is not below the specific value (NO), the flow rate of the fan pump is controlled so as to be the maximum flow rate (S26).
The method is a method of controlling the fan pump at a specific number of revolutions or less for acceleration performance in a zone where the number of revolutions is small and an amount of air is insufficient, but there is a limitation in that the condition of the zone where the number of revolutions of the engine is small needs to be basically satisfied, and further, because the method controls only the flow rate of the fan pump, the effect is not high. Therefore, the method is not appropriate as a method of adjusting torque when the construction machine such as the wheel loader accelerates.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.